Apparatus for lift-slab building construction



May 29, 1962 3,036,816

APPARATUS FOR LIFT-SLAB BUILDING CONSTRUCTION Original Filed March 20, 1956 A. H. STUBBS ETAL 4 Sheets-Sheet 1 NVENTORSJ ALLA/v H Sruees I Han 4190 Q use/g MW @W fln'aklveps.

May 29, 1962 A. H. STU-BBS ETAL 3,036,816

APPARATUS FOR LIFT SLAB BUILDING CONSTRUCTION Original Filed March 20, 1956 4 Sheets-Sheet 2 a E? INVENTORS. ALLAA/HSTUBBS,

1.111 HEW/m 5: misw AITdRN IS A. H. STUBBS ETAL 3,036,816

APPARATUS FOR LIFT-SLAB BUILDING CONSTRUCTION May 29, 1962 4 Sheets-Sheet 3 Original Filed March 20, 1956 INVENTORS ALAN/J1: $70655; 115mm 6. 11 /250;

mt rraeweys APPARATUS FOR LIFT-SLAB BUILDING CONSTRUCTION Original Filed March 20. 1956 May 29, 1962 A. H.'STUBBS ETAL 4 Sheets-Sheet 4 5 \%M% MW 2 4773211556;

United States Patent 8 Claims. (Cl. 254-89) The present invention relates generally to building con struction and more particularly to a type of construction known in the art as lift-slab construction.

This application is a divisional application of co-pending United States patent application, Serial No. 572,735, entitled, Method and Apparatus for Lift-Slab Building Construction, by Allan H. Stubbs, Edward K. Rice, and Howard G. Wilson, filed March 20, 1956, now abandoned.

Lift-slab building construction is that in which a plurality of horizontal slabs forming the various floors and the roof of a building are constructed of reinforced concrete poured at ground level with one slab resting on top of another and the slabs are thereafter lifted into their appropriate positions in the finished building. The lifting of the slabs is customarily accomplished by placing an hydraulic or other type of lifting jack on top of each of a plurality of columns in the building structure, and providing each jack with a cross member and dependent tension bars by which the slabs may be lifted by operating the jacks. This general method of construction is illustrated in Patent No. 1,006,436 to Pelzer.

In practicing the lift-slab method of construction above described it is desirable that the operation of the various jacks, placed on top of the columns, be so synchronized as to lift all portions of the slab at the same rate. It is further desirable that means be provided in conjunction with the tensile lifting members by which the same may be held motionless while the jack is lowered to take a new bite.

' A still further desirable characteristic of the lift-slab method is that in multiple stories where relatively tall slender columns are employed, that means he provided for progressively stiffening the columns during the lifting and as the slabs are raised into place.

With the foregoing general points in mind, it is a major object of the present invention to provide a system of slab-lifting jacks which are synchronized to provide automatic operation at a uniform rate.

It is a further object of the present invention to provide a system of the class described which does not require continual manual adjustment of the various jacks to provide the above-mentioned uniform and synchronous operation.

It is a still further object of the present invention to provide in a system of the class described a plurality of hydraulic jacks each of which is provided with its own separate hydraulic system whereby a failure of the power means leading from a central control point to the jack in question will not cause a failure of the jack itself. Such a system may be referred to as one which fails safe.

Yet a further object of the invention is to provide a system of safety interlocks which prevent operation of the lifting jacks in the event of a malfunction in the holding or lifting means.

An additional object of the invention is to provide an automatically operating tension member which is made up of separable sections whereby the unused sections may be removed as the lifting progresses.

A still further object of the invention is to provide a lifting system of the class described wherein diagonal bracing between successive slabs may be used to stiffen the structure as the slabs are progressively lifted.

The foregoing and additional objects and advantages of the invention will be apparent from a consideration of the following detailed description of certain presently preferred embodiments thereof, such consideration being given also to the attached drawings in which:

FIGURES 1, 2, and 3 are sequential perspective views illustrating successive stages of operation of the present method as employed in constructing a three-story buildmg;

FIGURE 4 is an enlarged elevational view taken through one of the columns shown in FIGURES 1 through 3, the same being partially sectioned to show the method of connecting the lifting and bracing means to the slabs;

FIGURE 5 is a bottom plan view taken on the line 5-5 of FIGURE 4;

FIGURE 6 is a top plan View taken on the line 66 of FIGURE 4;

FIGURE 7 is a fragmentary perspective view of a clamping mechanism employed in the jack structure shown in FIGURE 4;

FIGURE 8 is a semi-schematic diagram of a solenoid valve embodied in the lifting mechanism shown in FIG- URE 4;

FIGURE 9 is a semi-schematic elevational view of parts of the lifting jack shown in FIGURE 4;

FIGURE 10 is a side elevational view of the parts taken on the line 1010 in FIGURE 9; and

FIGURE 11 is a semi-schematic circuit diagram illustrating the jack synchronizing system embodied in the present invention.

Referring-first to FIGURES 1, 2, and 3, it will be seen that the illustrated building construction includes a foundation slab 20 poured at ground level, superimposed second and third floor slabs indicated at 21 and 22, respectively, and a roof slab illustrated at 23. The roof slab may, if desired, be formed with integrally molded beam portions shown at 24. In accordance with conventional practice, the slabs are separated by a bondinhibiting layer such as tar paper.

In the present illustrative embodiment the slabs 21, 22, and 23 in the finished building are supported on four pipe columns 30, each of which is in turn supported on a subterranean pier 31 to which it is secured by means of a lower terminal flange 32 and studs 33 (see FIGURE 4). The columns shown are conventional round pipe section, although it will be realized that other cross-section shapes can be used as desired.

A lifting collar 35 is embedded in each slab at each point where a colunm 30 passes therethrough. The collar 35 is provided with projecting flanges 36 which are perforated to receive tension members or lifting rods 38 and 39. The lifting rods 38 connect the uppermost slab 23 to the lifting jack to be described while the additional tension members 39 serve to interconnect sucessive slabs. The interior openings are formed of such size as to provide substantial clearance around each column to avoid frictional resistance when the slab is later raised.

Additional diagonally disposed interconnecting members 40 are employed to interconnect the spaced slabs. The diagonal members 40 are temporary only and are removed after the building has been completed, the temporary connection being effected by studs 41 embedded at appropriate points in the slab.

In the case of the present illustration, additional tension members to prevent sagging of the slabs at the points remote from the lifting columns are provided as shown at 43.

The details of the lifting jack, designated generally at 49, are best seen in FIGURE 4. Here it will be seen that a transversely extending jack base 50 is secured to the upper end of each of the columns 30. On each base 50 is mounted a conventional hydraulic jack cylinder 51, which cylinder contains a vertical piston or ram 52 to the upper end of which is secured a crosshead 53. The horizontal extent of the crosshead 53 is such as to project well beyond the sides of the column 30. The jack base 50 is in parallel alignment with the crosshead 53 and of equal horizontal extent.

Adjacent the outer ends of the crosshead 53 and the jack base 50 are mounted gripping mechanisms 54, the details of which may be seen in FIGURE 6. The operative members of the gripping mechanisms comprise a pair of jaws 55 and 56 which are urged toward each other by compression springs 57. The jaw members 55 and 56 are slidably supported in lateral track members 59 for transverse guided sliding movement on the top surface of the crosshead 53 (see FIGURE 7). The compression springs 57 are anchored against the rear edge of one of the jaws 55 and exert a closing force on the other jaw 56 by means of tension rods 58 which extend through loosely fitting transverse apertures in the jaw 55 and are secured to the jaw 56.

The jaws 55 and 56 are formed with adjoining semicircular recesses which together form an oval-shaped aper ture 59a through which passes the lifting rod or tension member 38. Secured to the crosshead 53 and to the jack base 50 below each aperture 59a is a tubular guide 591; which aligns the lifting rod 38 with the aperture 59a.

As can be seen in FIGURE 4, each of the lifting rods 38 is formed with a succession of spaced enlargements 60, the upper ends of which are frusto-conical as shown at 61. Thus it will be seen that as a lifting rod 38 is pulled upwardly through the gripping mechanism 54 the jaws 55 and 56 are separated by the engagement of the frustoconical portion 61 to open the jaws and permit the passage of the largest diameter of the enlargements 60. As a particular enlargement 60 passes the plane of the jaws 55 and 56 the later are snapped together by the action of the compression springs 57 and thus underlie the enlargement 60 to prevent relative downward movement of the lifting rod through the gripping mechanism.

From the foregoing description it will be appreciated that as the crosshead 53 is moved upwardly by operation of the jack piston 52 the gripping mechanisms 54 at the ends of the crosshead 53 engage the overlying enlargements on the rods 38 and exert tension on the rods. Conversely, when the crosshead 53 is lowered, the gripping mechanisms on the jack base 50 engage the rods 38 and prevent downward movement thereof while the gripping mechanisms on the crosshead 53, during the downward movement thereof, will automatically open and pass over the successive enlargements on the rods 38. Thus it will be seen that vertical'reciprocation of the jack piston 52 will automatically engage the rods 38 in a ratchet-like operation and incrementally lift the slab 23 to which the lower ends of the rods 38 are secured.

As the above-described operation continues and the slab is lifted by the rods 38, it will be seen that the latter extend a greater and greater distance above the jack 49 and that such upwardly projecting portion is unsupported against bending. Where the structure in question is only one or two stories in height the extended, unsupported rods are stiff enough to stand without bending. Where the rods exceed the length of two stories, however, they may tend to bend when standing alone. Also, the greater lengths are awkward to handle.

Accordingly, the rods 38 employed in the present illustration are each made up of several sections having threaded joints formed by boring and internally threading a terminal enlargement 60 as shown at 39a and forming an externally threaded extension 3917 on the end of the adjoining rod section. Thus the portions of the rod above the jack 49 may be unscrewed and removed as the lifting proceeds, as may best be seen in FIGURES 7 and 9.

Reciprocation of the jack piston 52 is accomplished by means of a double-acting hydraulic pump comprising two relatively small diameter pump cylinders 70 and 71 in which pump plungers 72 and 73 operate (see FIGURES 4 and 10). The details of the hydraulic jack, per se, being conventional, no further detailed description thereof is deemed necessary herein.

Reciprocation of the pump plungers 72 and 73 is effected by means of a rocker arm 74 fulcrumed at 75 on an upstanding pillow block 76 and connected to the plungers 72 and '73 by connecting links 77 and 78. The rocker arm 74 is provided with an outwardly extending lever 80, the outer end of which is pivotally secured to a piston rod 81 of a reciprocating air motor indicated generally at 82. To provide for the swinging movement of the lever about the fulcrum 75, the lower end of the air motor is pivotally secured to the jack base 50 as indicated at 83.

The air motor 82 is of more or less conventional design including a reciprocating piston 87 within the cylinder 84 which is driven back and forth between the ends of the cylinder by air admitted alternatively to one end or the other of the cylinder under the control of an electrically actuated valve 85. Air under pressure is supplied from a conventional source (not shown) by flexible conduit 86 and under the control of the valve 85 is admitted either directly from the valve 85 at the lower end of the cylinder 84 or through an interconnecting pipe 86 to the upper end of the cylinder 84.

While various types of electrically actuated valves are suitable for controlling the operation of the air motor 82 one suitable form is illustrated schematically in FIGURE 8. Here it will be seen that air under pressure admitted through a pressure manifold 90 is selectively directed to either of two cylinder conduits 91 or 92 by the longitudinal movement of a valve spool 93 mounted in the bore 94 of the valve. The bore 94 extends beyond the ends of the spool 93 whereby to form actuating chambers 95 and 96 adjacent the opposite ends of the valve spool 93.

Air under pressure is delivered to the actuating chambers 95 and 96 through passageways 97 and 98, respectively, each of which is provided with a flow restrictor 99. Air may be released from either of the actuating chambers 95 or 96 by opening a solenoid-operated pilot valve or 101, respectively. Release of air from either of the chambers 95 or 96 permits the pressure in the opposite chamber to move the valve toward the chamber from which air is released.

The construction and operation of the spool 93 is conventional and is shown in full line position in which pressure is delivered to the cylinder port 92 while at the same time the cylinder port 91 is connected to an exhaust port 102. Moving of the spool 93 to the position 93, shown in dotted line, reverses the operation, as shown by the dotted arrows delivering pressure from the manifold 98 to the'cylinder port 91 and exhausting the cylinder port 92 through the exhaust port 102.

It will be appreciated that the construction of the valve shown in FIGURE 7 is such that once the spool 93 has been moved to one or the other of its alternate positions it will remain in such position until the appropriate pilot valve 100 or 101 is opened to cause movement of the spool to its other position.

The air motor cylinder 84 is shown schematically in FIGURE 8 and it will be seen that the opposite ends are shown connected to the cylinder conduits 91 and 92 whereby the introduction of air under pressure at one end or the other of this cylinder 84 causes the piston 87 therein to move in one direction or the other, the air on the opposite side of the piston being exhausted through the appropriate port as previously described.

From the foregoing description it will be apparent that the air motor piston 87 is reciprocated back and forth in the cylinder 84 by alternatively opening the pilot valves 100 and 101. It is to be noted that these valves are opened only momentarily for a sufiicient time to release air from the associated actuating chamber 95 or 96. Due to the restriction 99 in the pressure delivery passages 97 and 98 air under pressure is not replaced in the actuating chamber therein so long as the pilot valve of such chamber is open.

Once the valve spool 93 has moved to its appropriate position and the pilot valve causing such motion is thereafter closed, the building up of equal pressure in both of the actuating chambers causes no return movement of the spool 93. Thus, once the pilot valves 1011 or 101 is pulsed, the valve spool 93 moves to the appropriate position causing the motor piston 87 to move to one end of the cylinder 84 where it remains until the valve spool 93 is actuated in the opposite direction.

As previously described, the air motor 82 is doubleacting since it is connected to two alternately operating pump plungers 72 and 73. Thus, each stroke of the piston 87, irrespective of direction, causes a power stroke of a pump plunger, thus raising the jack piston 52 by a small increment. Due to the relatively high mechanical advantage of the jack employed herein, the incremental movement of the jack piston 52 in response to a single stroke of the air motor 84 is on the order of of an inch.

The total stroke of the jack piston 52 from its lowermost position to its uppermost is on the order of 6 inches. The longitudinal spacing of the enlargements 611 along the lifting rods 38 is somewhat less than the full stroke of the jack whereby proper engagement of the jack with one of the enlargements 60 at each stroke of the jack is assured.

From the foregoing description, it will be realized that there is bound to be some variation in the speed with which various air motors in any system operate. For example, the load to be lifted may vary from point to point over the area of the slab or there may be variation in the friction losses in the compressed air conduits as between jacks close to and remote from the pressure source.

It is also apparent that a slab of concrete must be lifted at the same rate at all points if destructive stresses are to be avoided. Accordingly, synchronized operation within relatively close tolerances of all jacks is essential to successful operation of the lift-slab method Before proceeding to a detailed description of the circuit means by which the operation of the various jacks is synchronized, it is well to consider briefly the general principle employed. The total stroke of the jack piston 52 is divided into equal increments, in the present instance, twelve. interconnecting means are provided in the controls of the various air motors 82 whereby each jack stops upon reaching the end of the first increment of upward movement and remains stationary until all of the remaining jacks have reached the end of the first increment of motion, whereupon the air motors 82 automatically all start operating again. The first jack to complete the second increment of motion again pauses until the remaining jacks reach the end of the second increment, whereupon all jacks again move into the third increment and so on. The system is illustrated by showing only four jacks, designated No. 1, No. 2, No. 3, and No. 4, but it will be realized that any number of jacks can be synchroized by means of the system to be described.

For purposes of the discussion to follow the successive strokes of each air motor are designated as odd and even strokes, all those in a given direction being odd and all those in the opposite direction being even.

The above-described synchronization is effected by a series of cam-operated switches, one operatively connected to each of the jacks 49. The construction and arrange ment of these switches and their operating cams is illustrated semi-schematically in FIGURES 9 and l0.

On each of the jack bases 50 is secured an upstanding flat plate 110, which plate is provided with a central slot 111 which is parallel and co-extensive with the movement of the jack piston 52. Secured to the crosshead 53, and extending through the slot 111, is a cam mounting stud 112 on which is mounted a multi-lobed cam 113 arranged parallel to the slot 111 and on the opposite side of the plate 110 from the jack 49. A relatively short guide stud 114 is mounted on the lower end of the cam 113 and extends into the slot 111 to maintain the cam in a vertical position as it is moved by the jack piston 52 and the crosshead 53.

As can be seen in FIGURE 9, one edge of the cam 113 is provided with a plurality of sinusoidal cam lobes 115 which are of uniform height and are uniformally spaced along the length of the cam 113. A single pole, single throw, snap-action switch 116 is mounted on the front of the plate 110 and has an actuating lever 117 with a terminal roller 118 in contact with the operative edge of the cam 113.

The adjustment of the switch 116 is such that the switch is changed from one of its positions to the other each time the roller passes a. point halfway between the lowest dwell and highest rise on the cam. In the present illustrative embodiment the total jack stroke of 6 inches is divided by the cam into 12 equal increments, each of which is Well below the maximum difference in elevation that can safely exist between adjacent lift points in the slab during lifting.

Adjacent the upper end of the slot 111 is a single pole, single throw, normally closed limit switch 115 having an actuating button 1211 positioned to be engaged by the upper end of the cam 113 when the cam reaches the upper limit of its travel, As will be described, the purpose of the limit switch 119 is to render the jack inoperative upon reaching the upper end of its stroke.

The jack synchronizing circuit is illustrated in FI URE 11, which is a schematic block diagram in which the location of parts on the drawing is not necessarily the actual physical arrangement of the parts in the system.

Electric power to operate the system is provided in a conventional power supply 120, the main output of which is a power bus 121 which in the present instance is at 28 volts above ground, the other side of the power output being grounded as indicated at 122. Power from the supply 120 is also delivered to a square wave generator 125. The square wave generator is of conventional design and circuitry, being adapted to deliver two square Wave pulse signals denominated herein as the odd and even pulse signals which appear on output conductors 126 and 127, respectively.

The odd and even pulses are in 180 time displacement, as indicated graphically at 128 and 129 in the drawings. The odd and even pulse signals are delivered to odd and even pulse relay coils 130 and 13 1 so as to energize the respective relay coils upon the occurence of each pulse in the signal.

The actuating coils of the pilot valves 1410 and 161 previously described are indicated by those respective reference characters in FIGURE 11. The coil of pilot valve 1120 is energized each time the pulse relay 13-1 is energized, closing the contacts 132, thus to deliver power from the bus 121 through a conductor 133 to the coil and thence to ground. It will be noted that except as the even pulse signal may be interrupted by opening the limit switch 119, which is interposed in the conductor 133, even pulses are continuously delivered to the coil 100.

As previously stated, it is desired to interrupt the operation of each jack upon its reaching the end of a given increment of motion (unless it is the last jack to reach the end of such increment). Such control is effected by interrupting the odd pulse signal delivered to. the coil of the pilot valve 101. It will be appreciated that all that is required to interrupt the operation of the air motor is to interrupt one of the two pulse signals delivered to the pilot valves associated with such jack. The continued even pulse signal, which is delivered to a given jack, will be ineitective to produce any operation unless the even pulses are interspersed with odd pulses so as to return the piston 87 to the other end of the cylinder 84.

The cam-actuated interlock switch 116 is a single pole, single throw switch which, as shown in FIGURE 11, is arranged to interrupt a circuit from the power bus 121 through a relay coil 135 denominated herein the interlock relay. As will be described, energization of the interlock relay 135 or conversely, de-energization thereof, serves to interrupt the operation of the air motor by interrupting the odd pulse signal delivered to the pilot valve coil 101.

The odd pulse signal produced by closure of the contacts 136 each time the coil 130 is energized, is delivered selectively through contacts 137 or 138 of a pulse bus selector relay, the coil of which is shown at 139 in FIGURE 11. Since one of the two pairs of contacts 137 and 138 is normally open and the other is normally closed, it will be appreciated that when the coil 139 is energized, the odd pulse signal is delivered through a conductor 140 to an A pulse bus 141 whereas when the coil 139 is de-energized, the odd pulse signal is delivered to a B bus 142. Thus the odd pulse signal is present on only one of the two buses 141 and 142, the selector relay 139 alternately transferring the connection, as will be described.

The odd pulse present on one of the buses 141 or 142, for example the A bus 141, may reach the coil 101 only when the appropriate one of two pairs of contacts 143 and 144 of the interlock relay is closed.

As can be seen in FIGURE 11, the interlock relay is alternately energized and de-energized by the operation of the interlock switch 116 operated by the cam 113 as the jack moves upwardly. Thus, the contacts 143 and 144 are each successively closed and opened in alternate time phase whereby to connect the coil 101 through the conductor 145 alternately to the A bus or the B bus. It will be seen that assuming the signals to be reachingthe coil 101 through the appropriate pulse bus 141 or 142 and the appropriate pair of contacts 143 or 144, a change in the then condition of the interlock relay 135 will interrupt the pulse signal to the coil 101 until the pulse signal is again transferred from one of the buses 14 1 and 142 to the other.

The pulse bus selector relay 139 is operated in response to the relative positions of the various jacks in respect to their movement in a particular increment of motion. As previously described, each of the jacks in a system embodying the present invention is provided with a cam actuated switch 116 and its associated relay 135. Each of the relays 135 operates four pairs of contacts, to-wit: the two signal selector pairs 143 and 144 previously described and additionally two pairs of contacts for controlling the operation of the pulse bus selector relay, the latter two pairs being designated at 145 and 146, respectively, in FIGURE 11.

Inasmuch as many of the circuit elements associated with a particular jack are merely duplicated with respect to the other jacks, such duplicated circuit elements have not all been repeated in the drawings. The elements included within the phantom outline 147 are all of those associated with jack number 1 of the four jacks illustrated in the present embodiment, and it will be understood that the equivalent circuit arrangement containing the same elements is duplicated for each of the other three jacks, as indicated schematically by the phantom outline 148.

Two of the pairs of contacts actuated by the interlock relay 135 are concerned in the control of the pulse bus selector relay 139 and for this reason these contacts for each of the four jacks have all been shown in the drawings, are identified by the reference characters 145 and 146, and additionally by the designation K-li, K-Z, K-3 and K-4, identifying the same with jacks No. 1, No. 2, No. 3 and N0. 4, respectively.

The contact pairs 14 for the respective jacks K-1, K-2, K-3 and K-4 are all connected in series with a normally closed pair of contacts 150 of the selector relay 139 and a normally closed manual switch 154 to com plete a circuit from the power bus 121 through the pulse bus selector relay coil 139 to ground.

Thus, it will be seen that as the jacks successively reach the end of their first increment of motion, actuating their respective interlock switches 116, the contacts are successively closed, completing the above-described series circuit upon closure of the last pair of contacts. Completion of this circuit energizes the pulse bus selector relay coil 139, which, as earlier described, operates the contact pairs 137 and 138 and switches the odd pulse signal from the B pulse bus to the A pulse bus. This operation, as previously described, serves to re-start all of the air motors by switching the pulse signal to the bus to which each coil 101 is now connected, (the contact pairs 144 now being closed).

Energization of the pulse bus selector relay 139 also serves to open its normally closed contacts and close a pair of normally open contacts 151 to provide looking current, as will be described. Opening of the normally closed contacts 150 breaks the series circuit and thus momentarily interrupts the current to the pulse bus selector relay 139. In order to maintain the energization of the coil 139 for a sufficient time to cause the contacts 151 to become closed to lock the relay a condenser 15?. is connected across the coil 139.

The respective contacts 146 of the several interlocking relays 135 are, as shown in FIGURE 11, connected in parallel and form with the locking contacts 151 a parallelseries circuit delivering power from the power bus 121 to the pulse bus selector relay coil 139. Thus, it will be seen that so long as any one of the contacts 146 is closed, current is delivered to the pulse bus selector relay and the odd pulse signal remains connected to the A pulse bus.

Throughout the second increment of travel of any particular jack, the parallel contacts 146 associated with such jack remain closed. With a jack reaches the end of its second increment of travel the interlock switch 116 is again opened, de-energizing the relay 135 and, among other things, opening the associated contact pair 146. When all of the contacts 146 have been opened, the abovementioned parallel-series circuit is broken and the pulse bus selector relay 139 is de-energized, transferring the odd pulse signal from the A bus back to the B bus.

Therefore, as was the case in the first increment of motion of the jacks, each jack pauses upon reaching the end of the second increment due to the fact that the de-energization of the interlock relay 135 again transfers the connection of the coil 101 to the pulse signal bus upon which no signal is then present. By the time the last jack has reached the end of its second increment of travel, however, the signal is transferred to the bus to which all coils 10 1 are now connected, whereupon all jacks again start to operate. The sequence of operations at the end of the third increment of jack travel correspond, of course, to those of the first increment of travel wherefore the jacks continue their synchronized movement until they all reach the tops of their respective strokes.

When any jack reaches the uppermost limit of its stroke, the cam 113 engages the normally closed limit switch 119, breaking the circuit through the conductor 133 to the coil 100. Such jack then becomes inoperative until the crosshead therein is lowered to its starting position, permitting the switch 119 to close.

During the initial adjustment of the jacks before the lifting operation starts, and also at the end of the lift, it may be desirable to operate one or more of the jacks independently of the others. In the course of such operation, it is sometimes desirable to change the mode of the pulse bus selector relay, that is, to change it from its then condition to the opposite condition, whereby to transfer the signal from the A bus to the B bus, or vice versa. To accomplish this result, the two manually operable switches 153 and 154- are provided. By opening the normally closed switch 154, the pulse bus selector relay coil is de-energized, permitting the contact pairs 13 7, 138, 150 and 151 thereof to return to the position shown in full line in FIGURE 11. Conversely, closure of the normally open switch 153 energizes the coil 139 and moves the contact pairs 137, 138, 150 and 151 to the positions opposite those shown in FIGURE 11.

When all of the jacks have completed their full stroke, conventional fluid release valves in the jacks are opened to permit the jack piston 52 and the crosshead -53 to descend to its starting position so as to take a new bite on the lifting rods 33. As a safety feature, it is, of course, highly desirable that the jacks be prevented from descending if the lower gripping mechanisms 54, mounted on the ends of the jack base 50, are not properly closed. Accordingly, the fluid release valves of the jacks 49 are solenoid-operated under the control of a normally closed safety switch 160, mounted adjacent the jaw 55 of the lower gripping mechanisms. Thus, if either of the jaws 55 is opened, the circuit through the switches 160 is broken and it is impossible to open the fluid release valve in the jack in question.

All of the foregoing control circuit elements, except the cam-operated switches 116 and the limit switches 119, are located in a central console (not shown) from which three conductor signal cables radiate to each of the jacks. The three conductors of each signal cable, it will be realized, are those shown in FIGURE 11 as connecting the elements in the upper part of the area 147 with those in the lower part thereof.

The details of construction and some of the operations of the invention having been described, the overall operation of lifting the three slabs shown in FIGURE 1 into their appropriate positions in the finished building may now be described. The initial steps of pouring the slabs into their superimposed positions shown in FIG- URE 1 are conventional and need not be described in detail herein. Sufiice it to say that some separatory medium such as tar paper or lacquer is applied to the interfaces between the successive slabs so that they may be separated during the lifting operation.

Also it will be noted that at the time the slabs 241, 22, and 23 are poured, nuts or other similar fastening members 19 are embedded in the concrete under the apertures in the collars 35, so as to receive the threaded ends of the lifting rods I38 or other tension members 39'.

When the slabs have been cured to reach their full strength, the lifting operation is commenced by connecting the lifting rods 3% to the roof slab 23- and to the jacks 49 mounted on the top of the columns. The lifting of the roof slab 23 then commences and continues as previously described until the spacing between the two slabs 22 and 23 is equal to that which will be obtained in the finished building. At this point, the lifting operation is interrupted and interconnecting rods 39' and t3 and diagonal braces 4 are secured between the slabs 22 and 26 as previously described. In this connection, it will be noted that the tension members 43 are attached to the upper slab at the apex of the inverted beam 24 whereby to transfer the stiffening effect of the beam 24 to the slab 22.

The interconnections having been made as just described, the lifting operation is again commenced and continued until the slab 22 is at its appropriate spacing from the slab 21, at which time the lifting operation is again interrupted. Interconnecting members 39, 43 and diagonal braces 40 are now connected between the slags Z1 and 22 and the lifting operation reactivated until the slabs 21, 22 and 23 all reach their final position. At this point the lifting operation is stopped with the slabs preferably positioned slightly above their final position in the building, and suitable abutments are welded to the columns 30 below each of the collars 35. Each of the jacks may then be released through the operation of manual release valves (not shown), lowering the slab slightly onto the just-mentioned abutments. The lifting operation i now complete and all tension members, jacks, etc. may be removed.

It will be realized that the just-described method is particularly adapted for the lifting of multi-story slabs in that the relatively long and slender columns 30 are progressively stiffened as added load is applied thereto. This stifiening is particularly effective, since the diagonal interbracing of the slabs at substantial spacing from each other provides an effective guide to prevent bowing or lateral bending of the columns 30.

While the method and apparatus hereinabove described is illustrative of the invention is fully capable of achieving the objects and providing the advantages hereinbefore stated, it will be realized that both the method and the apparatus are capable of considerable modification without departure from the spirit of the invention. For this reason we do not mean to be limited to the forms shown and described, but rather to the scope of the appended claims.

What is claimed is:

1. Apparatus for constructing lift-slab structures comprising: a plurality of jacks adapted for connection to a lift-slab at horizontally spaced lift points therein; a motor connected to each of said jacks to operate the same, each motor being adapted to operate in response to a signal and stop when said signal is interrupted; a signal generator; a signal conductor for each motor connecting the same to said signal generator; a signal interrupter interposed in each conductor; and an actuator for each interrupter, said actuator being carried by a moving portion of the jack operated by its corresponding motor, said actuators being adapted to actuate their respective interrupters and interrupt said signal and stop when said motor upon said jack reaches the end of a given increment of lifting movement, said increments for all of said jacks being equal whereby to prevent any lift point in said slab be ing lifted higher than another by more than said increment.

2. For use in raising lift-slabs, a system of synchronized jacks comprising: a plurality of jacks adapted for connection to a lift-slab at a plurality of spaced lift points; a plurality of motors, one for each jack, and connected thereto to operate the same, each motor being adapted to operate in response to a signal and stop when said signal is interrupted; a signal generator; a plurality of first signal conductors, each connecting said generator with a different one of said motors; a plurality of first signal interrupters, one interposed in each of said first conductors; a plurality of actuators for said first interrupters, one carried by a moving portion of each of said jacks, each of said actuators being operatively associated with the corresponding one of said interrupters to actuate the latter and interrupt said signal to stop said motor n said jack reaching the end of a given increment of lifting movement, said increments for all of said jacks being equal whereby to prevent any lift point in said slab from being lifted higher than another by more than said increment; a plurality of second signal conductors, motors and each being independent ofsaid first interrupters; a plurality of second interrupters, one interposed in each of said second conductors and in normally open condition; and means connecting said actuators to said second interrupters to close the same upon the associated jack reaching the end of said increment whereby said motors are all connected to said second conductor when said jacks all reach the end of said first increment; and signal transfer means interposed between said generator and said conductors and adapted to transfer said signal from said first conductor to said second conductor when all of said jacks have reached the end of said first increment of movement.

3. Apparatus for constructing lift-slab structures comprising: a plurality of slab-lifting jacks, each adapted to be supported on top of a column in a lift-slab building and having tension means adapted to be secured to a slab to be lifted at a lift point adjacent the base of said column; a plurality of motors, one for each jack and connected thereto to operate the same, each motor being adapted to operate in response to a signal and stop when said signal is interrupted; a signal generator; a plurality of separate signal transmission means, each connecting said generator with a different one of said motors; a plurality of signal interrupters, one interposed in each of said transmission means; and a plurality of actuating means for said interrupters, one carried by a moving portion of each of said jacks, each of said actuating means being operatively associated with a corresponding one of said interrupters to actuate the latter and interrupt said signal to stop said motor upon said jack reaching the end of a given increment of lifting movement, said increments for all of said jacks being equal whereby to prevent any lift point in said slab being lifted higher than another by more than said increment,

4. Apparatus for constructing lift-slab structures comprising: a plurality of slab-lifting jacks, each adapted to be supported on top of a column in a lift-slab building and having tension means adapted to be secured to a slab to be lifted at a lift point adjacent the base of said column; a plurality of motors, one for each jack and connected thereto to operate the same, ach motor being adapted to operate in response to a signal and stop when said signal is interrupted; a signal generator; a plurality of separate signal transmission means, each connecting said generator with a different one of said motors; a plurality of signal interrupters, one interposed in each of said transmission means; a plurality of actuating means for said interrupters, one carried by a moving portion of each of said jacks, each of said actuating means being operatively associated with a corresponding one of said interrupters to actuate the latter and interrupt said signal to stop the associated motor upon the associated jack reaching the end of a given increment of lifting movement, said increments for all of said jacks being equal whereby to prevent any lift point in said slab being lifted higher than another by more than said increment; and lift reinst-ituting means comprising a plurality of elements, one operatively associated with each of said actuating means to be actuated upon said associated jack reaching the end of said increment, all said elements being interconnected to re-establish said transmission means and start all of said motors when all of said jacks have reached the end of said increment.

5. For use in raising lift-slabs, a system of synchronized jacks comprising: a plurality of jacks adapted for connection to a lift-slab at a plurality of spaced lift points; a plurality of motors, one connected to each jack to operate the same, each motor being adapted to operate its respective jack in response to a signal applied thereto and to stop upon interruption of said signal; a signal generator; a pair of signal conductors; first signal transfer means adapted to apply said signal from said generator selectively to one or the other of said signal conductors; a plurality of second signal transfer means, one for each of said motors and each adapted to connect its respective motor selectively to one or the other of said conductors; a plurality of actuatable synchronizng elements, one for the motor of each jack, each element being connected to a respective one of said second transfer means whereby to effect said transfer of said motor connection when said element is actuated; a plurality of actuators, each carried by a moving portion of a respective one of said jacks and adapted and connected to actuate the respective synchronizing element of such jack upon said respective jack reaching the end of a given increment of lifting movement; and signal control means operatively connected to all of said actuators and to said first signal transfer means to actuate the latter to transfer said signal from one to the other of said conductors whenever all of said jacks reach the end of a particular increment of travel.

6. In a lift-slab apparatus of the type having a plurality of horizontally spaced jacks connected to a horizontal slab to lift the same by said jacks acting in unison, control means for synchronizing the operation of said jacks comprising in combination: a plurality of motors, one connected to operate each jack, said motors each being adapted to operate during the application of a signal thereto and to remain inoperative in the absence of said signal; a plurality of separate actuator means each carried by one of said jacks and moved between alternate first and second positions con-responding to alternate successive increments of lifting movement of said jacks, said increments as to all jacks corresponding in number and size; a first group of circuit interrupters, each actuated by a respective one of said actuator means and normally closed when said actuator means is in said first position open when the same is in said second position; a second group of circuit interrupters, each actuated by a respective one of said actuator means and normally open when said actuator means is in said first position and closed when the same is in said second position; a signal generator; a first signal conductor connected to all of said motors through the respective interrupters of said first group; a second signal conductor connected to all of said motors through the respective interrupters of said second group; and signal transfer means responsive to the positions of said actuators to apply the signal from said generator to said first conductor during said first increment of motion and to transfer said signal to the conductor to which it is not then applied each time all of said jacks reach the end of a particular increment of motion.

7. The apparatus of claim 6 further characterized in that said signal transfer means includes: a third group of circuit interrupters, each actuated by a respective one of said actuator means and normally open when said actuator means is in said first position and closed when the same is in said second position; a fourth group of circuit interrupters each actuated by a respective one of said actuator means and normally open when said actuator means is in said first position and closed when the same is in said second position; relay means adapted whene energized to effect transfer of said signal from said first conductor to said second conductor, a circuit including all of said third group of interrupters connected in series to energize said relay means when all interrupters in said third group are closed; and a holding circuit for said relay means including all of the interrupters in said fourth group connected in parallel to maintain energization of said relay means until all interrupters of said fourth group are opened.

8. In lift-slab apparatus of the type having a plurality of horizontally spaced jacks connected to a horizontal slab to lift the same by said jacks acting in unison, control means for synchronizing the operation of said jacks comprislng in combination: a plurality of motors, one connected to operate each jack, said motors each being adapted to operate during the application thereto of an electric signal and to remain inoperative in the absence of said slgnal; a plurality of separate switch actuator means, each carried by one of said jacks and moved between alternate first and second positions corresponding to alternate successive increments of lifting movement of such jacks, said increments as to all jacks, corresponding in number and size; a first group of single pole, two-position switches, each actuated by a respective one of said actuator means and closed when said actuator means is in said first position; a second group of single pole, two-position switches, each actuated by a respective one of said actuator means and normally open when said actuator means is in said first position; a signal generator; a first signal bus connected to all of said motors through the respective switches of said first group; a second signal bus connected to all of 13 said motors through the respective switches of said second group; and a signal transfer relay having an operating coil and adapted to apply the output of said signal generator to said first signal bus when said operating coil is de-energized and to said second signal bus when said coil is energized; a third group of normally open switches connected in series, each adapted to be closed by a respec tive one of said acutator means upon the corresponding jack reaching the end of the first increment of travel; powered means for said relay coil connected through said third group of switches whereby to energize said coil when all of said jacks have reached the end of said first increment of travel; and locking means for said relay coil comprising a pair of locking contacts closed by said relay when energized and a plurality of switches connected in parallel with each other and in series with said locking contacts, each said last switch being adapted to be closed by a respective one of said switch actuating means when the latter is in said second position whereby to maintain the signal in said second bus until all jacks have reached the end of the corresponding increment of travel.

References Cited in the file of this patent UNITED STATES PATENTS 1,147,080 Dunlap et a1 July 20, 1915 1,327,611 Burns et a1. Jan. 13, 1920 1,398,822 Wilson Nov. 29, 1921 1,454,088 Thrift May 8, 1923 2,655,223 Villars Oct. 13, 1953 2,758,467 Brown et a1 Aug. 14, 1956 2,867,111 Youtz Jan. 6, 1959 2,975,560 Leonard Mar. 21, 1961 

